I started work on colour mixing earlier
this year and had some promising results with a basic, manual setup. Things moved onto
other 3D printing developments and I got sidetracked for a few months.

Dual extrusion has been the focus for many
machines, but this has some significant problems of alignment and oozing of the
inactive hot-end and the fact you cant mix/blend materials with two separate hot-ends.

Background -

I always wanted a single hot-end with
multiple driven feeds, so that’s the focus of this particular development.Before I forget, the files for this project are up on Thingiverse here.

Another wonderful advanced example of layer
selective of colour printing has been this set of stunning 3D printed iPhone cases by Matthew Bennett (norcalbarney).

Photo and 3D printed iPhone cases by Matthew Bennett - Thingiverse

Seeing the work by Myles on the RepRap Blog
and the prints by Matthew spurred me to re-start and finish off my own rather elaborate colour
blending extruder development.

Stop-Start -

I had previously stopped my development because
I was having some issues getting two colours to mix well in the nozzle; I
introduced mixing slits and a spiral in the PTFE tubes (in and after the PEEK
block) and added steps in the nozzle barrel, it had reasonable mixing results
but was very tricky to make up by hand.

The same month I saw that Myles had exactly
the same issues with the black and white mixing I decided that not mixing the colours well would
produce more interesting effects and give more artistic looking prints. So during
#30DOC in June I restarted the development and added three feeder tubes. I had
initially intended these to be separately driven Cyan, Magenta and Yellow feed,
but after some testing realised that all sorts of blends could be made by
running single or multiple extruder's at intervals separately or together.

Unfortunately my Antique Lathe died in
February, which is one of the main reasons this multi-head hot-end didn’t get
further development, but with a bit of work I managed to do everything I needed
(all of the following below) with just a Pillar drill and hand-tools.

3-Way Hot-End - (Version 1 - ... it dies a bit later on, but bear with me, it gets better with V2)

Without a Lathe, I decided that I needed a simple
hot-end that clamped together; this would allow easy manufacture and
experimentation.

First steps were to make a simple over-sized heating block and using a step-drill I bored a stepped hole in the middle, 4mm at the bottom and 14mm at the top.

The nozzle is a M6 brass bolt with a 0.5mm hole, this is cut down to 8mm long and held in place with an M6 brass half nut.

The filament feed tubes would be held in
with a block of PEEK clamped down onto the heating block.

And clamped to the hot-end with a Stainless steel plate.

Nice and simple construction.

The PEEK block has three holes (you could
have more), drilled on a slight angle so they spiral into the stepped heating
block. It uses 4mm PTFE tubes to allow the extruders to be angled around the Quick-Fit
X-Axis plate.

I was aware this was not going to last a
long time, but I wanted something simple to test the idea with actual driven
extruders first.

I was expecting rope seal adhesive to be a
good way to bond the PTFE tubes into the PEEK, but this turned out to be a very
bad plan. Maybe my Rope seal is just no good, I still have yet to get any
reasonable results using it. Nophead however uses a different brand for bonding
his heating resistors without any issues at all, so I may revisit this compound
in the future.

Blending nozzle V1, assembled – the
Stainless plate is clamped to the heating block using long M3 Stainless screws,
the PEEK has some Copper tape wrapped around it to aid cooling.

This only has a single 6r8 Resistor, so takes a few minutes longer to get to temperature than a ‘standard’ sized heating block, but gives a good stable performance when insulated up.

First manual test, very easy to push the separate filaments by hand, this might just work!

I finished the manual tests and mounted it all on the printer, ready for test and calibration.
Testing each stepper driver, extruder, hot-end heating and thermistor feedback took about 1 hour.

I got it all working and 'calibrated' well enough for a first print, when... the hot-end assembly died. :(
It did print the striped heart box shown in the very first picture in this blog, then slowly the tubes started to pull out of the PEEK block.

The Glass rope adhesive was soft and had allowed the tubes to be pushed out, quite a mess.
I really think my glass rope adhesive is bad or out of date, it only ever seems to get semi-set no matter how long I leave it, even at elevated temperature.

Never mind, lesson learnt and I know exactly how I'm going to make the next one -

3-Way Hot-End - (Version 2 - ... the one that didn't die! and worked gloriously well)

The heating block and nozzle worked perfectly, so I'm re-using that. I just need to make a much better PEEK and tube holder -

Start with some raw materials, 4mm PTFE tubes, PEEK and Aluminium bars. I'm saving up for a new Lathe, but it's going to take a while to get a new one. So at this point I still only have a pillar drill and hand tools, here goes -

PEEK was cut, drilled, then filed and sanded in the Pillar drill to get a domed plug.

Aluminium bar was also cut, drilled and grooved (with a hack saw!) all rotating in the Pillar drill. (who needs a Lathe!)... - I still do actually :(

Holes are tapped M4 threads.

Use a pencil sharpener on one end of each tube, just cut a little.

Picture shows, normal tube at the bottom, lightly sanded (500 grit) middle, top is threaded (see below)
Before you try to cut the thread on a PTFE tube it VERY important that you lightly sand the outer surface of the tube or you will never be able to grip and turn it in the die!

It's quite easy to cut the thread, you can use a piece of sand paper to grip on the sanded tube while you rotate it in the die, don't cut too fast and go both directions.

You do not need to use the liquid PTFE, but I had some and wanted to try it out.

The thread is more than enough to hold in the tube, but I wanted to see if the Liquid PTFE made it easier or harder to screw the tube into the PEEK.

It did add some lubrication, but does not seem to make much difference, most of the Liquid is pushed out, but I feel a little happier knowing it was added.

All done, let it dry and trim the tubes at a 45 degree angle to each other and to the walls of the heating block.

Once cut you must drill/ream out the PTFE tubes back to be 2mm internal bore, it will have narrowed due to the threading and fitting into the PEEK block. Do this very carefully and make sure you remove all the PTFE swarf.Then you can assemble it.

This time the stainless plate is clamping both the aluminium heat-sink and PEEK, this works exceptionally well, the Aluminium block stays warm and can be fan cooled if required, Stainless plate is cold.

New V2 hot-end and extruder assembly.I know what you are thinking, how heavy is that lot! well it's not as bad as you would think, the extruders are lighter because of the
Nema14 motors, but still, it's a significant weight - Note:- I'm running this on my BIG MendelMax using M8 smooth rods and it's still working fine.

I'm getting an X/Y travel speed of 170mm sec without any issues at all on my bigger MendelMax, I changed the acceleration down in firmware to 4000mm/sec, and set X/Y jerk to 15mm/sec.

I have tested print speeds of between 20mm/sec and 65mm/sec at the moment. It seems to be most happy at around 45mm/sec and a 1.4mm extruder retraction. (using 3 x 1.75mm Faberdashery filaments)

Electronics Expansion -

Ideally you would need to drive all three
(or more) extruder's as separate outputs from the firmware and send sets of
Gcode commands to enable and mix the colours for the object being printed.
That’s all future stuff and quite doable as the next stage.

For now I'm using my standard RAMPS 1.3 setup with a modified Sanguinololu PCB to act as a stepper expansion board.

I decided as a first development to expand
a single Extruder channel to drive 4 separate stepper drivers and control these
stepper enable lines separately so filament blending could be tested with just
standard Gcode and normal firmware. Slightly crude, but simple and very effective.

You still need to populate some components on the Sanguinololu, and fit Pololu or stepstick drivers. Components around the steppers are required, including the Microstepping select jumpers, these should be set to whatever your normal Extruder drive is set (mine are x8)

You do need to make sure each extruder
drive has a separate enable line. Some are shared on the Sanguinolou, so cut
the tracks to make them separate.

Also use a 4k7 resistor for the enable
pull-ups as the main controller has a very weak pull-up (100k) already fitted on the enable line, if you don't fit smaller ones on this expansion board it won't switch the extruder's off quickly when you disable them.

You only need 5 wires coming from the original Extruder driver, Step, Dir, Enable, and +5V.The Sanguinololu board must have +12V and GND connected to it's normal power rail input.

The 3 separate extruder drivers on the
Sangunnolo are controlled by the single enable line from the main electronics.
For ease of testing the enable line can therefore be switched on or off for
each extruder. Spare output pins from the micro could easily be used for
enabling each extruder, but for a proof of concept, switches allow the easiest
way to experiment and evaluate performance and operation.Make sure you set the trim-pot reference
voltages to about 0.42v for NEMA14 motors if you are using Pololu setpper
drivers. If you are using Stepsticks, that’s turned about 95% of the way around
(about 1A)

All ready to go...Setting the Firmware-

Now that 1, 2 or 3 extruder's will be driven
together, you need to set the Esteps in firmware

For me the Esteps are 360 (x8 micro-stepping) for one extruder. So if you want to run a single extruder at a time and switch individually between them, 360 is the correct number.More interestingly you can run any two extruder's at the same time, so the two filaments are combined / blended together, you still have three output combinations and it's actually possible to swap out the 3rd inactive filament for a different colour while it's printing using the other two, then switch to another set of two extruder's using the new colour/material. to do that the Esteps need to be half the value as you have two feeds both giving half the volume to the nozzl, 1/2 of the number above = 180And finally running all three at a time can give some great looking prints and different colours from each direction of the object! to do that you will need 1/3 of the Estep value = 120It's easier to see the different effects in the video than in the pictures below, but take a look at both.

Video Part 2 - Construction and Prints -

Prints!-

You must be wanting to see some prints by now :) - Here you go -

Single extruder feed at a time, Gold, Red and Blue filaments used.

Single extruder feed at a time, Gold, Red and Purple filaments used.

More pots, Single extruder at a time.

The one at the back also had a colour swap of gold for the last section.

Two extruder's at a time, Pink, Blue and Pearl White filaments used.

You can see in this picture, that Pearl White is the common colour and Pink and Blue are alternated as the print progresses. (Ignore the yellow outline, that was the purge from the previous used colours)

This picture shows the two extruder colours and how they work on a printed object, this is the same part just rotated 180 degrees, using Orange and Silver filaments.

I used up all my 1.75mm filament stock in these test prints, but I'm keen to build up a whole printer in glorious multi-colour blended wonderfulness!

And Imagine using different materials, soft PLA for modifying hardness or doing a flexible 'hinge' in the part. or Glow in the Dark with a hint of whatever colour you like for daytime and night viewing.
Mixing both ABS and PLA together would be an interesting experiment, maybe one to try at some point.

For now more work getting the electronics a little more integrated and maybe a multi-fed Bowden version?

Other news -

Raspberries -
I had the pleasure of presenting at the recent Raspberry Jam in Bristol on Monday this week, (not 3D printing this time around, but maybe next time) it was a splendid evening and we had some really great presentations and demo's. Thanks to everyone that came for the Jam.

And a big thank you to Patrick for giving me one of his first really nice Laser-cut (home-made) Acrylic Raspberry Pi cases. If you don't want to print one, you can get hold of his very nice version here -

Clay -
I do get lots of messages about the Universal paste extruder, thanks and keep them coming, and I am planning on doing much more, both on clay and other materials and also the Peristaltic pump extruder as soon as I can.
I do have Metal clay to try and also Paperclay (very good for low warp - perfect 3D printing material)

Rostock -
Finally I need to mention the Rostock delta printer. If you don't already know?, go and read all about it , Right now, it's totally Awesome with a really big A.

Thanks as always for reading, and please post a comment or contact me to say what you think.

Tremendous work Rich! Fantastic looking prints. They are like chameleons changing colour. Pushing the envelope again. Well done!

I notice you moved to NEMA14 motors. They are obviously powerful enough. What it for weight reduction? Do you think they are strong enough to push 3mm filament also?Did you consider a Bowden triple rig, keeping the weight off the x-carriage? Why might you have ruled that out?Regards,NumberSix

Thanks Ivor, I do really like the 'toothpaste' look, I have printed a few machine parts and I must say they look great.

The NEMA14's are good, they work very well for 1.75mm filament. Not tried them with 3mm, but I expect that's asking a bit much if you want to print fast at a reasonably low temperature to reduce ooze. So I would say not.

I'm planning a Bowden version, May work very well on Sublime's Tantillus I backed his Indiegogo campaign, the kit is on it's way to me :)

I am still surprised how fast the travel moves are, I think it could go higher, it's just a bit scary moving that fast!

Couple of things: I really love the toothpaste prints, I have seen similar things when putting multiple colors of clay in a single syringe without mixing. The color comes out toothpaste style and the nice thing is that when the extruder moves one way, color A is on top, if it moves the opposite direction color B is on top. This pattern repeats but also iterates because the colors never come out perfectly on the same side, they swirl. Maybe its more systematic in a hot end but in a large diameter syringe there is a lot of changing around. You can see an old example here, I am experimenting a bit in the future: http://unfold.be/system/uploads/551/full/LAE_Vases6.JPG?1335532920 The one in front is terracotta and white clay mixed. The two clays have totally different properties but in a way they fire perfect when mixed like this.In regards to the metal clay printing. I have specifically build your extruder for doing tests with this since my large syringe air pressure operated system is a bit overkill and there is not much room for tuning the pressure when silver is flowing out and it was a nice test case to throw your extruder at :) I have been using the paste version of PMC since it comes loaded in a 10cc syringe. I tested first with the hard clay you have but its hard to control viscosity, I would advise putting it in a zip bag with a drop of water and leaving it overnight to soften, knead in the bag and add another drop till its good. Small drops at a time. I have made a small adapter that 'converts' 10cc syringes to 20cc for use in the extruder. The big problem is that the prints sag substantially when using the paste so maybe the clay is better when softened but make sure to make it as stiff as possible. I have spend a couple of days and 200€ clay but still not there :). The money issue is very problematic, there is no room for much material spilling and you are through 100€ in silver material in 30 minutes. What you need to do is recycle every bad print, every speck and spill. Again, throw it in a bag with little drop of water and it will soften again. Knead and reuse. You will have less scarcity issues with the copper but I believe its much harder to recycle because it oxidizes (silver and gold don't). I will now try and make my own silver clay, its cheaper and you can control the viscosity better. Maybe a different faster drying organic binder? Looking forward to your results with the metal clay.

Wow, thanks for the tips, I had a very hard time getting the clay mixed well in my first experiments, I'll try the Zip bag trick, that sounds perfect.

I got the Copper and Bronze just really for testing the idea before using the expensive silver, I would love to know how well your own silver clay comes out. It also looks like copper is a bit trickier to fire, but it'll be a good practice material.

When I made the first nozzle I tried to make them swirl around inside, with the second version I cut the tubes at 45 degrees and made no other attempt to make them mix. Adrian Bowyer and Myles Corbett had a lot of issues trying to get them to mix passively, even Stainless steel mesh inside the nozzle does almost nothing to assist in the mixing.

I think the 'toothpaste' look is more unique at this point for 3D printing, maybe in time we will have fine blending and mixing of many materials.

Great post. A bit of a contrast to my blog where everything is white these days! Do you get any problem with each colour needing a different temperature? I am thinking of fire truck red and lapis blue which are poles apart.

I wonder if instead of three motors, drivers and some switches it could be done with one motor and a gearbox with three gear levers giving 1, 1/2 and 1/3 ratios.

I had imagined a lot more issues with temperatures, and the first colours I started with were Red, White and Blue. It's actually quite odd but I have not changed temperature the entire time during testing (about 80 hours printing) with almost every faberdashery material, including some really odd ones. I have managed a constant 186 degrees C for everything regardless of speed or number of extruder's being enabled.

I was starting to think it maybe because I have a chamber in the Aluminium hot-end below the feed tubes and PEEK block this fills with plastic and may thermally assist with the balance. This does give me a little bit of ooze, but I'm just about overcoming that with travel speed and retract.

I would love to try out a lot more different nozzle designs to see if a version can be made without such a big chamber as this takes a little time to purge at the moment. But then maybe temperature will be an issue?

It would be really great to do a mechanical version, but I guess you would need a bigger motor to drive all 3 filaments at once. It could well be the best way to do 5 or 6 feeds. And a fixed Nozzle with moving bed would really help with filament management!

Very nice results! Maybe using something like a static mixer (http://en.wikipedia.org/wiki/Static_mixer, http://www.koflo.com/static-mixers.html) could help getting even more consistently mixed colors. Not sure they work with ABS or PLA, though.

It should work well with PLA, most static mixers require many stages and high pressure to get a good mix.Adrian Bowyer and Myles Corbett did investigate static mixers and made some prototypes for passive mixing, it seems a tricky thing to do in a small hot-end.I do have a small chamber in the hot-end so I could try to fit a machined labyrinth slug, but this will increase the extrusion pressure required.

I was actively looking for someone to make me a hotend i could do this on and it was either "too hard" or "too expensive", though I would have thought you'd have to be nozzle size at the end of every filament tube and then have them all meet at either the nozzle or very close to it to avoid the filaments from applying too much pressure to each other and to avoid "lag"... Also, was there a reason for not going bowden?

Hi and Thanks! I know what you mean, it does look like I'm going a little bonkers some times, Just high on RepRap! And you gotta think outside the dodecahedron :)

I'm not a great programmer, so I would really love to see more work done on the software for multiple extruder's - I didn't mention in the post that Slic3r 0.9.1 now has support for 'many' extruder's hopefully it won't be long before we see some more support in the firmware and tool-chains to do great things with two or more extruder's.

I have been looking at shared signals for two driver boards so that I can independently control my two zmotors for auto-leveling and tweaking. The plan that I seem to never get around to implementing is to make a fake driver board which acts more like a plug and have that wire over to a second board where the two drivers live. The idea being that it would not require modification of the original board. From there the plan was to break the STEP signal instead of the ENABLE signal to switch between drivers. I want to go with STEP so that both drivers remain enabled.

Just wondering if you can think of a reason why using STEP instead of ENABLE might not work out.

Hi Billy, That is a nice idea to be able to adjust each Z motor to do an auto level, the only issue is that you would need two end-stops for the Z? making a modification and change to the FW. If you only use one Z stop and your Z is level but the bed is not, you may end up building wonky parts.

I'll need to check the data sheet, you may get noise/jitter or random steps if you switch the Step signal. You would need a pull-up at least to stop it floating.

I would still say that doing an 1 to 2 expander driver with a second Z endstop and spare pin controlling the second enable is your best option, especially with Z as you don't need to keep them enabled all the time. You'r spare pins could come from unused Y+ & Z+ endstop connections so they were easy to connect too. You could still make it retro-fit then.

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I have to say I wish I were as good at this kind of thing as you. That is amazing what you did making this printer. I have a hard enough time just getting mine to work at all. I'm always tempted to just go buy another one. I don't think I've ever thought that I could just make one.

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It is very good job! If you want a specific time to extrude a specific color how could you implement this? You extrude somewhere the old color and then begin the new? Can you calculate how much color you need for a specific part so when the color changes you dont need to waste the old color. Thank you very much for sharing!(i hope you understand my English).

A few questions:It looks like there are 6 hinges on your roostock+ printer, none of which actually use bearings, just metal rubbing on plastic. Is this going to introduce wear problems?

The braided fishing line: how did that workout as a drive mechanism? I figured you'd roll it up on one side of a spindle as you unrolled it from the other side. I had concerns that the winding would make it nonlinear. Do you think the stuff would be strong enough for a CNC machine?

Do you have any solution for driving the steppers separate now, or are you still driving them as one stepper in the g-code?It seems like you could drive two sepatate stepper channels from the ramps 1.4, maybe that´s part of the soulution?

(sorry for my bad english, i don´t speak it normally and is still learning in school.)

first of all i am very much impressed of your work...but now i need help bro....i am trying do the same but cannot figure out the connections you have soldered on the board.can you help me briefly with the connec tions....another question is that you have said that the stepper controller you used is ramp 1.3....i have ramp 1.4 so will it works??another thing i want to know is that actually how the 3 colours are actually controlled??i mean is the any change in firmware or the code??i am very new to this...please help me

I love those set of stunning 3D printed iPhone cases by Matthew Bennet. Are those products of filament mixing? I’m surprised about the effects and artistic looking prints it yielded. Since I’m no good in this kind of printing technique, I’m contented using various colours of this http://www.3d2print.net/shop/3d-printer-filament/elastic-filament/ for 3D printing phone cases.

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Congratulations!!! You did a great job! I would like to know if you would sell your extruder or if there are any ecommerce site that I can buy this technology? Thank you for all contribution you made to 3d printer technology.